Positive electrode active material particle including core containing lithium cobalt oxide and coating layer containing boron and fluorine, and preparation method thereof
Provided is a positive electrode active material particle including a core containing lithium cobalt oxide represented by the following Chemical Formula 1; and a coating layer containing boron (B) and fluorine (F), which is coated on the surface of the core: Li 1+x Co 1−x O 2 (1)
1. A positive electrode active material particle, comprising
a core including lithium cobalt oxide represented by the following Chemical Formula 1; and
a coating layer including boron (B) and fluorine (F), which is coated on the surface of the core:
Li 1+x Co 1−x O 2 (1)
wherein −0.03≤x≤0.1, and
wherein lithium in the core is in an excessive amount.
2. The positive electrode active material particle of claim 1 , wherein in the coating layer, the boron and fluorine form a chemical bond with lithium.
3. The positive electrode active material particle of claim 1 , wherein the boron and fluorine form a chemical bond with lithium of the core.
4. The positive electrode active material particle of claim 1 , wherein the boron and fluorine exist in a compound of forming a chemical bond with lithium, independently of the core.
5. The positive electrode active material particle of claim 2 , wherein the boron and fluorine, together with lithium, exist as LiBF 4 .
6. The positive electrode active material particle of claim 1 , wherein a weight of the coating layer is 0.5% by weight to 5% by weight with respect to a weight of the core.
7. The positive electrode active material particle of claim 1 , wherein the positive electrode active material particle exhibits a capacity retention rate of 90% or more, as measured in a coin-type half cell at an upper voltage limit of 4.5 V at 45° C. during 50 cycles.
8. A method of preparing a positive electrode active material particle for a secondary battery, the method comprising:
(a) preparing a first lithium cobalt oxide represented by the following Chemical Formula 2;
Li 1+y Co 1−y O 2 (2)
(wherein −0.03≤y≤0.1)
(b) dry-mixing the first lithium cobalt oxide and a first compound including all of boron and fluorine, or dry-mixing the first lithium cobalt oxide, a second compound including boron, and a third compound including fluorine; and
(c) heat-treating the mixture after the dry-mixing of (b).
9. The method of claim 8 , wherein the first compound is one or more selected from the group consisting of NH 4 BF 4 , NaBF 4 , (CH 3 ) 3 O(BF 4 ), (C 2 H 5 ) 4 N(BF 4 ), (C 6 H 5 ) 3 C(BF 4 ), (CH 3 ) 4 N(BF 4 ), (CH 3 CH 2 CH 2 ) 4 N(BF 4 ), and C 3 H 10 BF 4 P.
10. The method of claim 8 , wherein the second compound is one or more selected from the group consisting of B 2 O 3 , H 3 BO 3 , (C 6 H 5 O) 3 B, B 2 H 4 O 4 , C 6 H 5 B(OH) 2 , CH 3 OC 6 H 4 B(OH) 2 , and C 6 H 12 BNO 3 .
11. The method of claim 8 , wherein the third compound is one or more selected from the group consisting of NH 4 HF 2 , NH 4 F, (CH 3 ) 4 NF, (CH 3 CH 2 ) 4 NF, PVdF (polyvinylidene fluoride), PVdF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene)), PVF (polyvinyl fluoride), PTFE (polytetrafluoroethylene) and ETFE (ethylene tetrafluoroethylene).
12. The method of claim 8 , wherein the dry-mixing of (b) is performed by high energy milling.
13. The method of claim 8 , wherein the heat-treatment of (c) is performed at 300° C. to 600° C.
14. The method of claim 8 , wherein the heat-treatment of (c) is performed at 450° C. to 500° C.
15. The method of claim 8 , wherein the heat-treatment of (c) is performed for 3 hours to 7 hours.
16. A secondary battery comprising a positive electrode including the positive electrode active material particle of claim 1 , a negative electrode, and an electrolyte.
17. The secondary battery of claim 16 , wherein the electrolyte includes LiPF 6 as a lithium salt, and PF 5 which is a decomposition product of LiPF 6 reacts with a coating layer of the positive electrode active material particle to be converted into PF 6 − which is a less reactive anion than PF 5 .
18. The secondary battery of claim 16 , wherein at least part of the coating layer of the positive electrode active material particle is dissolved into the electrolyte.
19. A battery pack comprising the secondary battery of claim 16 .
20. A device comprising the battery pack of claim 19 .
21. A positive electrode active material particle, comprising
a core including lithium cobalt oxide represented by the following Chemical Formula 1; and
a coating layer including boron (B) and fluorine (F), which is coated on the surface of the core:
Li 1+x Co 1−x O 2 (1)
wherein −0.03≤x≤0.1, and
wherein a weight of the coating layer is 0.5% by weight to 5% by weight with respect to a weight of the core.